A General View
"The earth is the mother of us all-plants, animals and men. The phosphorus and calcium of the earth build our skeletons and nervous systems. Everything else our bodies need except air and sun comes from the earth."
Henry A. Wallace, in the Foreword to "Soils and Men," the 1938 Yearbook of the United States Department of Agriculture.

Without soils, no life could exist on earth. The lowly bacterial cell and the massive pachyderm both owe their being to this basic stuff of life. A bird in flight, a mole burrowing beneath your lawn, borers eating blindly into the heart of a great oak-all are linked by their common dependency on the elements of existence they draw from the soil.

Of all the earth's living creatures, man alone manipulates and modifies the land to better suit his ends. Not satisfied with soil as he finds it, he tears its surface, incorporates organic and mineral mate­rials and alters age-old structures. He often keys his actions to two false but widely held ideas: 1, that soils are simply clay and decaying vegetable matter-a mechanical support for plants-and 2, that the easy-digging quality of the soil means more than its chemical-bio­logical quality. The error of this over-all viewpoint was thrown into sharp focus not so many years ago by the controversy concerning the use of synthetic chemical soil conditioners. These products often made soil easier to till but with no resulting improvement in quality of plant growth. The "organocultists," those who believe only in organic gardening, have much to say about all this. Their ideas are aired in a later chapter.

Soil type is important. Type is determined largely by texture, a word often used in the wrong sense. It means simply particle size, such as fine sand, gravel, silt, clay, and so on.

Particle sizes in soils range something like this (mm = millimeter; 25 millimeters equal one inch):

Mineral elements:
Clay............ 002 mm or smaller
Silt ............ 002 mm to .05 mm
Fine sand............ 05 mm to .25 mm
Sand ............ 25 mm to 1.0 mm
Gravel............ 1.0 mm to 32 mm
Stones............ over 32 mm

Organic matter in soils may range in size from as large as entire plants that have been dug under to as small as humus particles so fine that they form colloidal solutions. (In a colloidal solution the minute particles do not settle out, but float indefinitely.)

Based on the preceding information, here is a soil classification according to particle size (comments are explained throughout the book):

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